1. Field of the Invention
The present invention relates to a front end module for processing transmission signals and reception signals in a communications device such as a cellular phone.
2. Description of the Related Art
Third-generation cellular phones have been introduced and it is getting required that such phones have not only the speech function but also the high-speed data communications function. Therefore, in various countries, adoption of a variety of multiplexing systems for achieving high-speed data communications is considered. In the current situation, however, it is difficult to unify the multiplexing systems. Consequently, it is required that the cellular phones be provided for multiple modes (systems) and multiple bands.
In Europe, for example, dual-band cellular phones operable under the global system for mobile communications (GSM) and the digital cellular system (DCS) have been used in the entire region. Each of the GSM and the DCS is a time division multiple access system. In Europe, as the third-generation cellular phones, it is expected that dual-mode, triple-band cellular phones are adopted, which are operable under the wideband code division multiple access (W-CDMA) capable of implementing a high data communication speed (2 Mbps, for example), in addition to the above-mentioned two systems.
If new functions as described above are added to the cellular phones, the circuits are more complicated and the number of components increases. Higher-density mounting techniques are thus required for the cellular phones. Under such a circumstance, it is necessary to achieve a reduction in size and weight of the components and to achieve combination and integration of the components for the high frequency circuits inside the cellular phones to reduce the mounting space.
The Published Unexamined Japanese Patent Application Heisei 11-225088 (1999) discloses a high frequency switch module for the dual-band cellular phones operable in the GSM and the DCS. This high frequency switch module separates the frequency band corresponding to the GSM and the frequency band corresponding to the DCS from each other through the use of a branching circuit, and separates transmission signals and reception signals in each of the frequency bands from each other through the use of two high frequency switches.
The Published Unexamined Japanese Patent Application 2002-43977 discloses a high frequency module for processing transmission signals and reception signals of each of three communications systems using three frequency bands. This high frequency module separates a low frequency band from a high frequency band through the use of a diplexer. The high frequency band includes the two frequency bands of the first and second communications systems. The low frequency band includes the frequency band of the third communications system. A first high frequency switch separates the reception signals of the first and second communications systems from the transmission signals of the first and second communications systems. A second high frequency switch separates the transmission signals and the reception signals of the third communications system from each other. Two SAW filters separate the reception signals of the first communications system from the reception signals of the second communications system. In addition, the Published Unexamined Japanese Patent Application 2002-43977 discloses that the components of the high frequency module are integrated through the use of a layered structure made up of a plurality of stacked sheet layers.
According to the high frequency switch module disclosed in the Published Unexamined Japanese Patent Application Heisei 11-225088, the high frequency switches are used to separate the transmission signals and the reception signals in each of the frequency bands from each other. According to the high frequency module disclosed in the Published Unexamined Japanese Patent Application 2002-43977, the high frequency switches are used to separate the transmission signals and the reception signals from each other, too. Therefore, the high frequency switch modules disclosed in those publications have a problem that they are not operable in the CDMA.
In the Published Unexamined Japanese Patent Application 2002-43977 the duplexers including two SAW filters for separating the reception signals of two communications systems are called SAW duplexers. However, duplexers generally mean those for separating transmission signals and reception signals from each other. In the embodiments of the invention those for separating transmission signals and reception signals from each other are called duplexers, too. Therefore, the SAW duplexers disclosed in the Published Unexamined Japanese Patent Application 2002-43977 are different from the duplexers of the embodiments of the present invention, in terms of function.